Warning Signs of a Cardiac Emergency: What to Look For and When to Act
Written by Stephanie Austin, Owner and Lead Trainer, Prima Cura Training | Last reviewed: August 2026 | Next review: August 2027
Part three of three. Read part one: Heart Attack vs Cardiac Arrest | Read part two: Ventricular Fibrillation and Cardiac Arrest.
The first two posts in this series covered the differences between a heart attack and cardiac arrest, then went deeper into ventricular fibrillation and what AEDs are actually doing. Both were about understanding what is happening once an emergency is already unfolding.
This one is about the moments before that.
Because the most important thing about a cardiac emergency is not knowing the medical terminology. It is knowing when something is wrong. Recognising the signs early and acting on them without hesitation is what gives someone the best possible chance. If you just need the quick answers, jump to the FAQs.
Some of the warning signs are well known. Some are far less so. And some of the most dangerous ones are the ones most commonly dismissed as something else.
At a Glance: Heart Attack vs Cardiac Arrest Signs
| Heart Attack | Cardiac Arrest | |
| Onset | Symptoms often build gradually, sometimes over hours | Usually sudden, with little or no warning |
| Consciousness | Person is awake and responsive | Person collapses and is unresponsive |
| Breathing | Normal or laboured | Absent or only gasping (agonal breathing) |
| Skin colour | May become pale, grey or clammy | Typically pale, grey or bluish |
| Pain? | Often yes: chest, arm, jaw, back, stomach | Not typically: they are already unconscious |
| Call 999? | Yes, immediately | Yes, immediately |
| Start CPR? | No, unless they deteriorate into cardiac arrest | Yes, straight away |
The Warning Signs of a Heart Attack
A heart attack is a medical emergency from the moment it begins. But unlike cardiac arrest, it does not always announce itself dramatically. The symptoms can build gradually, sometimes over hours, and because they can feel vague or inconsistent, people regularly convince themselves it is probably nothing.
It is not.
The classic warning signs of a heart attack include:
- Chest pain, pressure, tightness, or discomfort. Often described as a heaviness, squeezing, or a weight pressing on the chest. It may radiate or stay in one place.
- Pain spreading to the left arm, shoulder, jaw, neck, back, or stomach.
- Shortness of breath, with or without chest discomfort.
- Sweating, particularly a cold or clammy sweat that comes on suddenly.
- Nausea or vomiting.
- Light-headedness or dizziness.
- Pale, grey, or bluish skin. On darker skin tones, this can be easier to see on the palms of the hands. Updated NHS guidance (March 2026) lists this explicitly.
- A sense of impending doom. This is a recognised clinical symptom and should not be dismissed or felt embarrassed about reporting.
Not everyone will have all of these. Some people will have two or three. Some will have chest pain that comes and goes. Some will have pain that feels nothing like the classic “crushing” description. None of that makes it less serious.
The Symptoms That Often Get Missed
| This section matters. Read it carefully. Heart attack symptoms in women, older adults, and people with diabetes can present very differently from the textbook description. That difference has cost lives. |
Women are more likely to experience heart attacks with atypical symptoms: nausea, unusual fatigue, shortness of breath, back or jaw pain, or a general feeling of being seriously unwell, without pronounced chest pain. The European Resuscitation Council 2025 First Aid Guidelines note that around a quarter of women report jaw pain, nausea, or shortness of breath instead of the classic symptoms. These are more easily attributed to anxiety, indigestion, or exhaustion. Research published by NHS England shows that women are around 50% more likely to receive an incorrect initial diagnosis when having a heart attack, with average treatment delays significantly longer than for men. The symptoms deserve the same urgency, regardless of gender.
People with diabetes may have reduced pain sensitivity due to nerve damage (neuropathy), which means they can experience a heart attack with little or no chest pain at all. Shortness of breath, unexplained fatigue, or a sudden deterioration in blood sugar control may be the only signs. The ERC 2025 guidance notes that this group may express pain in the epigastric region or present with shortness of breath alone.
Older adults may present with confusion, extreme fatigue, or a general deterioration rather than classic chest pain. The symptom profile can resemble other conditions, which is partly why recognition is sometimes delayed.
The rule is clear: if something feels wrong, act as though it is. The cost of calling 999 when it turns out to be indigestion is a little embarrassment. The cost of not calling 999 when it turns out to be a heart attack is a great deal more than that.
What Is a Silent Heart Attack?
A silent heart attack, known medically as a silent myocardial infarction, is one that occurs with minimal, vague, or no recognisable symptoms at all. The person may feel briefly unwell, slightly breathless, or experience mild discomfort they put down to a pulled muscle or acid reflux. The event passes, and they assume nothing serious happened.
Silent heart attacks are more common than many people realise, particularly in women, older adults, and people with diabetes. The damage to the heart muscle is the same as in a symptomatic heart attack. The risk of a subsequent cardiac event is also the same.
This is not included to alarm anyone. It is included because it reinforces the same point: any unusual or persistent symptom involving the chest, breathing, or a general sense that something is not right deserves a proper medical assessment, not a decision to wait and see.
Warning Signs That Can Appear Days Before
This is one of the less widely known aspects of cardiac emergencies, and it is worth knowing about because it can prompt someone to seek help before a crisis develops.
Prodromal symptoms are early warning signs that can appear in the days or even weeks before a heart attack. Research published in the journal Circulation has found that a significant proportion of heart attack patients, particularly women, reported unusual symptoms in the period beforehand that they did not connect to their heart at the time.
The most commonly reported prodromal symptoms include:
- Unusual or unexplained fatigue. Not ordinary tiredness, but a profound exhaustion that does not resolve with rest.
- Sleep disturbance that appears without an obvious cause.
- Shortness of breath with minimal or no physical exertion.
- Indigestion, nausea, or stomach discomfort that has no clear dietary explanation.
- Chest discomfort that comes and goes and does not feel severe enough to be alarming.
None of these is specific to heart attacks on its own. But a combination of them, particularly in someone with known risk factors such as high blood pressure, high cholesterol, diabetes, smoking, obesity, or a family history of heart disease, should prompt a conversation with a GP rather than a decision to leave it.
The Warning Signs of Cardiac Arrest
Cardiac arrest presents very differently from a heart attack. In most cases, there are no gradual warning signs. The person collapses suddenly, is unresponsive, and stops breathing normally. There may be occasional gasping breaths, known as agonal breathing, but these are not effective breathing and should not be mistaken for normal respiration.
If someone is unresponsive and not breathing normally, that is cardiac arrest. You do not need a diagnosis. You do not need to identify the underlying rhythm. You need to call 999 and start CPR.
The Resuscitation Council UK 2025 Guidelines note that patients with both in-hospital and out-of-hospital cardiac arrest often have premonitory signs. Some people do experience symptoms in the minutes immediately before cardiac arrest: sudden dizziness, chest discomfort, or palpitations. But these are brief, inconsistent, and not always present. For the purposes of recognising and responding to cardiac arrest, the check is simple: unresponsive and not breathing normally. That is enough information to act.
The 2025 Guidelines also update a key point for lay rescuers: if someone is unresponsive, call 999 before assessing breathing. This ensures emergency services are alerted at the earliest opportunity, and call handlers can guide you through the next steps.
| Not sure about the difference between a heart attack and cardiac arrest? The first post in this series covers both conditions in detail, including exactly what to do in each situation. |
When Should You Call 999?
The answer is simpler than most people expect.
Call 999 immediately if:
- Someone is unresponsive and not breathing normally (start CPR while you wait)
- Someone has chest pain lasting more than a few minutes, or pain that comes and goes
- Someone has chest pain alongside any other symptom: breathlessness, sweating, nausea, arm or jaw pain
- Something feels seriously wrong, even if the symptoms do not match a textbook description
Do not:
- Drive to A&E yourself. Paramedics can begin treatment on the way. A car cannot.
- Wait to see if it gets better. With a heart attack, time is heart muscle. Every minute of delay matters.
- Assume it is probably nothing. The cost of calling 999 unnecessarily is minimal. The cost of not calling when it matters is not.
What to Do While You Wait for the Ambulance
The Resuscitation Council UK 2025 First Aid Guidelines set out clear guidance for what to do between calling 999 and the ambulance arriving.
For a suspected heart attack:
- Help the person sit or lie down comfortably. Do not let them walk around.
- Loosen any tight clothing around the chest and neck.
- Aspirin: The 2025 guidelines confirm that if the person has cardiac-sounding chest pain and is not allergic to aspirin, you should encourage and assist them to chew and swallow 300mg of aspirin (ideally chewable or dissolvable) as soon as possible, whilst awaiting emergency help. This recommendation aligns with current NHS guidance.
- If the person has been prescribed angina medication such as a GTN spray, assist them in using it as directed.
- Do not give food or drink.
- Stay with them and keep them calm. Do not leave them alone.
- Monitor closely: if they lose consciousness and stop breathing normally, start CPR immediately.
For cardiac arrest:
- Start CPR immediately. Push hard and fast in the centre of the chest, 100 to 120 compressions per minute, 5 to 6 centimetres deep.
- If an AED (defibrillator) is available, get it and use it straight away. Follow the voice prompts.
- The 999 call handler can guide you through every step if you need support.
The Most Common Reason People Do Not Act in Time
Research consistently shows that one of the biggest contributors to poor outcomes in cardiac emergencies is not the absence of a bystander or the distance from the hospital. It is hesitation. People wait. They do not want to cause a fuss. They tell themselves it is probably indigestion. They look to others in the room for a cue to act, and find that everyone else is doing the same thing.
That hesitation is understandable. And it costs lives.
The Resuscitation Council UK 2025 data shows that NHS ambulance services attempt resuscitation in around 43,000 people each year in England. Bystander CPR is provided in 60 to 73% of cases, but AEDs are used in under 10%. With trained CPR and prompt action, survival to 30 days can be as high as 30%. Without it, the overall figure sits at around 9 to 10%.
The confusion between conditions is part of it. If you are not sure what a heart attack looks like, or how it differs from cardiac arrest, or what either of those has to do with the AED on the wall at work, you are more likely to pause. That uncertainty is exactly why this series exists.
But even with the knowledge, the instinct to wait for certainty before acting is one of the hardest things to override. So here is the most useful thing anyone can take from all three posts:
| You do not need to be certain. You need to act. Call 999. Start CPR if the person is unresponsive and not breathing normally. Let the professionals make the clinical diagnosis. Your job is to recognise that something is wrong and respond to it. Doing something is always better than waiting for certainty that may not come. |
Who Is at Higher Risk?
Knowing your risk factors does not prevent a cardiac emergency, but it does give useful context for taking symptoms seriously rather than brushing them aside.
The main risk factors for heart attack and sudden cardiac arrest include:
- High blood pressure (hypertension)
- High cholesterol
- Type 2 diabetes
- Smoking
- Obesity or being significantly overweight
- Physical inactivity
- Excessive alcohol consumption
- A family history of heart disease or sudden cardiac death
- Age: risk increases with age, and significantly so for women after the menopause
Some causes of sudden cardiac arrest, particularly in younger people and athletes, involve inherited electrical conditions of the heart with no obvious prior symptoms. This is one reason why defibrillators in schools and public spaces are not optional extras. According to the Resuscitation Council UK, coronary heart disease is responsible for around 80% of sudden cardiac deaths, while in younger individuals the main causes include inherited heart diseases, congenital heart defects, and myocarditis.
Knowledge Is the First Step. Training Is What Makes It Stick.
Reading about cardiac emergencies builds awareness. Training builds the muscle memory and confidence that holds up under pressure, when someone is on the floor in front of you, and you need to act without stopping to think.
In every course I run, whether that is a one-day qualification or an in-depth programme, learners leave understanding not just what to do but why. Because that understanding is what turns hesitation into action.
Basic Life Support and AED | Emergency First Aid at Work (EFAW) | First Aid at Work (FAW)
Get in touch: info@primacuratraining.co.uk | 0333 999 8783
Frequently Asked Questions
What are the most common warning signs of a heart attack?
The most common warning signs include chest pain, pressure, or tightness; pain spreading to the arm, jaw, neck, back, or stomach; shortness of breath; sweating; nausea; pale, grey, or bluish skin; and dizziness. Symptoms vary significantly between individuals. Not everyone will experience chest pain, and not everyone will have severe symptoms. Any combination of these signs, particularly if they persist or come and go over more than a few minutes, is a reason to call 999. Current NHS guidance on heart attack symptoms confirms this.
Can women experience different heart attack symptoms from men?
Yes. Women are more likely to experience atypical symptoms such as unusual fatigue, nausea, back or jaw pain, and shortness of breath, without pronounced chest pain. These symptoms are easier to dismiss, which is one reason heart attacks in women are sometimes recognised and treated later than in men. The British Heart Foundation has detailed guidance on heart attack signs in women. The symptoms deserve the same urgency regardless of gender.
How do I tell the difference between a heart attack and cardiac arrest?
During a heart attack, the person is usually conscious, able to speak, and still breathing. During cardiac arrest, the person collapses, becomes unresponsive, and stops breathing normally. If someone is unresponsive and not breathing normally, treat it as cardiac arrest: call 999 and start CPR immediately. For the full explanation of both conditions, see part one of this series.
What are prodromal symptoms and should I take them seriously?
Prodromal symptoms are early warning signs that can appear in the days or weeks before a heart attack. They include unusual fatigue, sleep disturbance, shortness of breath, and intermittent chest discomfort. They are not specific enough on their own to confirm an impending heart attack, but they are worth taking seriously, particularly in anyone with known cardiac risk factors. If in doubt, speak to a GP rather than waiting.
Should I call 999 even if I am not sure it is a cardiac emergency?
Yes. If something seems seriously wrong, particularly involving the chest, breathing, or sudden unresponsiveness, call 999. Paramedics can begin assessment and treatment on the way to the hospital. If it turns out not to be a cardiac emergency, no harm is done. The risk of not calling when it is one is not worth taking
What should I do while waiting for the ambulance after calling 999 for a heart attack?
Help the person sit or lie down comfortably, loosen any tight clothing around the chest and neck, and keep them calm. Do not give food or drink. Do not let them walk around. The Resuscitation Council UK 2025 First Aid Guidelines confirm that if the person is not allergic to aspirin, encourage them to chew and swallow 300mg as soon as possible. Monitor closely: if they lose consciousness and stop breathing normally, begin CPR immediately.
Is it safe to do CPR if I have not been trained?
Yes. Compression-only CPR, pushing hard and fast in the centre of the chest, is better than doing nothing. The 999 call handler will guide you through it in real time. If you have received Basic Life Support training, deliver both chest compressions and rescue breaths if you are trained and willing to do so. The Resuscitation Council UK 2025 Guidelines confirm that untrained bystanders will be guided through compression-only CPR by call handlers, and that trained rescuers should give rescue breaths if they are confident to do so.
This article is intended for general information purposes only and does not constitute medical advice. All information reflects current NHS guidance, Resuscitation Council UK 2025 Guidelines, and clinical best practice at the time of writing and is correct as of August 2026. Anyone experiencing potential symptoms of a cardiac emergency should call 999 immediately and not rely on this article for diagnosis or treatment decisions. Guidance is subject to change; always refer to current official sources including nhs.uk and resus.org.uk.
